Onondaga Lake in Syracuse, New York, has historical significance as the site of the founding of the Haudenosaunee (Iroquois) Confederacy and literary ________ as the setting for some of the legends of Hiawatha.

First of all, kudo for the perfect question in terms of: formatting, tags and so on. Perfect.

Back to the question: this one could be solved by POE.

A certain site (does not matter where is located of what we are talking about) is the center or the origin of certain legends.

Now: acumen means sharpness, pragmatism is an approach, fortitude is courage, and relativism is an attitude. As such, import means meaning, so import is the meaning, the center, the origin of certain legends from that site aforementioned.